102 MASS. EXPERIMENT STATION BULLETIN 185. 



one of the enzymes that are beUeved to be necessary for the production 

 of sap colors in plants. 



O is the factor for dark mottling in mottled beans, in the absence of 

 which we have the light mottled type of the Horticultural class, provided 

 P, Y and Z are all present. 



X represents a blackening factor found only in Creaseback. 



The remaining letters of the formula are the determiners which in the 

 presence of other necessary factors determine the color of the seed coat. 

 The significance of the colors is as follows: G, black; F, coffee brown; 

 C, yellow; E, dark red; D, light red (see page 84). 



Summary. 



It is evident from these and other investigations that the inheritance of 

 seed coat color in beans is very comphcated, and difficult to explain fully 

 and satisfactorily. The problems involved are interesting, and the plants 

 convenient to handle for purposes of investigation. They provide excel- 

 lent material for the fruitful investigation of Mendelian inheritance. 



In this work 21 varieties have been used in making over 120 different 

 crosses, involving more than 40,000 plants. The work continued over a 

 period of eight years. 



There are certain correlations in the pigmentation of the plant. All 

 white or eyed beans are accompanied by white flowers; all black or black 

 mottled beans by dark pink flowers. Mottled beans, other than black 

 mottled beans and those of various yellow and brown colors, are usually 

 accompanied by Hght pink flowers. 



In a general way the crosses of pigmented and white beans show a 3:1 

 ratio, but there are some rather wide departures which may or may not 

 be of genetic significance. 



The inheritance of mottling may be explained by the double factor 

 hypothesis of Emerson and Spillman. Crosses of two mottled varieties 

 have in all cases given only mottled progeny. Crosses of mottled and 

 self-colored varieties have yielded mottled beans in Fj, and the parent 

 types in a 3:1 ratio in F2. Crosses of mottled and white varieties have 

 given mottled beans in Fi, and usually mottled, self-colored and white in 

 a 9:3:4 proportion in F2. 



In most cases crosses of two self-colored varieties have given only self- 

 colored progeny. The principal exceptional variety is Blue Pod Butter, 

 which, when crossed with most self-colored varieties, yields mottled 

 progeny none of which breed true to the mottled character. White vari- 

 eties may carry the character for mottling, which can show itself only 

 after crossing with a pigmented sort. Creaseback is peculiar in that it 

 seems to carry factors for mottling and an additional factor causing a 

 blackenmg which nearly or quite obscures the mottled pattern. 



There are two types of mottling, — the dark, seen in Red Valentine and 

 Refugee and many others, and the light, seen in varieties of the Horticul- 

 tural class. The former behaves towards the latter as a simple dominant. 



